The present invention relates to a data transmission apparatus and method, a data receiving apparatus and method, and a data transmission and reception system and method, which are used for transmission and reception of data.
In recent years, digital signals are becoming increasingly used for transmission and recording of audio and image data. For example, in digital satellite broadcasts, digital signals are compressed and transmitted through the use of satellites. The digital satellite broadcast is highly resistant to noise and fading and can transmit higher-quality signals in comparison with existing analog broadcasts. Also, recently, as typified by optical disks, magneto-optic disks, etc., recording media capable of recording digital signals have been developed in increasing numbers. As a result, for example, it has become possible to digitally record digital signals transmitted by the above-mentioned digital satellite broadcast in an ordinary household. Furthermore, it is also possible to digitally record digital signals played back from a recording medium, such as an optical disk, for digital data through a bus, etc.
In the meantime, in digital signals, since signal deterioration barely occurs during the transmission of signals, it is possible to copy data at a quality which is essentially equivalent to that of the original. For this reason, the risk of illicit data copying is high, and protection of copyrights might not be ensured.
Accordingly, methods for protecting digital data have been conventionally proposed. For example, there is a method for setting a flag, which prohibits copying of data, in data to be transmitted. This is such that, on the data transmission side, when data from which copying should be prohibited is to be transmitted, data is transmitted with the flag which prohibits copying being set, and in the recording apparatus on the receiving side, apparatus control is performed such that recording of data is prohibited according to the setting or non-setting of the flag. In this case, for example, at the first copying of data, the flag for copying prohibition is not set, and for example, the flag is set when a recording medium in which data is copied is copied onto another recording medium. As a result, one-time-only copying is possible, but copying of data is not possible from the copied recording medium to a second or subsequent medium.
However, in the method for setting a flag in data in a manner as described above, there is a problem in that protection of data cannot be sufficiently ensured unless the recording apparatus on the receiving side is designed to handle processing of the flag. That is, when there is an apparatus which can receive data without recognizing the flag and which can record the data, the protection of the copyright cannot be ensured. Also, if the flag is rewritten by using a computer, any number of copies can be made.
In the meantime, in recording media for digital data, which are commercially available, a method is adopted in which data is compressed by a predetermined compression method and is recorded. When such digital signals recorded in recording media are to be digitally recorded on another recording medium through a bus, etc., usually, compressed data is once decoded into non-compressed data on the data transmission side, and the data is compressed again on the data receiving side and digital recording is performed. When compression of data is repeated several times in this manner, deterioration of data may occur, depending upon the performance of the apparatus which compresses the data.
However, in recent years, a method has been proposed in which received compressed data is digitally recorded on a recording medium as it is without decoding or compressing the data. In the case of this method, since a data compression process needs not be performed on the recording side, signal deterioration barely occurs in practice during the recording of the data. Therefore, with regard to such a method, in particular, it is necessary to focus on protecting copyrights.